1. Field of the Invention
The present invention relates to a power supply apparatus provided with a power supply circuit for generating a DC output.
2. Description of the Related Art
A power supply apparatus such as an AC/DC converter, a DC/DC converter, a charger, etc. is popular in various fields. Generally, a power supply apparatus should be small in losses. Particularly, it is very important to reduce losses in a power supply apparatus used in a portable personal computer, a terminal unit in a mobile communications device, etc.
A personal computer, etc. normally demands different voltages. In response to this demand, a number of power supply apparatuses are designed to generate different voltages. Additionally, since various portable electric appliances are normally battery-powered, there are a large number of power supply apparatuses equipped with a charging function.
FIG. 1 shows the configuration of an example of a conventional power supply apparatus. The power supply apparatus comprises a charger 501 for charging a battery (not shown in FIG. 1) with electric energy, and plural DC power supplies 502-1 through 502-4 for providing electric currents for loads (not shown in FIG. 1).
A processor (MPU) 503 is an operating unit for controlling the operation of the power supply apparatus, and it communicates with a higher order appliance, controls a sequence, manages a battery, monitors and displays a state, etc. For example, when the power supply apparatus is provided in a computer, a higher order appliance can be the CPU (main processor) of the computer. When the processor 503 receives from the higher order unit, for example, an instruction to change a voltage level, it notifies the corresponding DC power supply of the instruction. The sequence control is a process in which the power is sequentially supplied to or disconnected from the plural DC power supplies 502-1 through 502-4 in a predetermined order. The battery control is the function of monitoring the residual charge in a battery, etc. The state monitor/display is the function of monitoring the input voltage to the power supply apparatus and the environmental temperature, and displaying them as necessary.
FIG. 2 shows the configuration of the charger or the DC power supply provided in the conventional power supply apparatus. The charger and the DC power supply basically have the same configurations, and individually include an electric power converter 510, an analog circuit unit 520, and a signal transmission/reception unit 530. In this example, the DC power supply is a DC/DC converter.
The electric power converter 510 includes a switching element (MOSFET) controlled according to the instruction from the PWM control circuit 524; a rectifying diode; an inductor for storing/discharging energy; a resistor for detecting an inductor current or an output current; and an output capacitor for smoothing an output. While the switching element is in an ON state, the inductor current ramps up with the electric current provided for the load, thereby storing residual charge in the output capacitor. On the other hand, while the switching element is in an OFF state, the inductor current ramps down and the electric charge stored in the output capacitor is discharged as necessary with the electric current provided for the load.
The analog circuit unit 520 includes an amplifier 521 for amplifying an inductor current or an output current; an amplifier 522 for amplifying the difference between the output from the amplifier 521 and a reference voltage Vref1; an amplifier 523 for amplifying the difference between the output voltage and a reference voltage Vref2, a PWM control circuit 524 for generating a PWM signal for controlling the switching element based on the output from these amplifiers, etc.; and an oscillator 525 for providing a clock at a predetermined frequency to the PWM control circuit 524.
When the output voltage becomes lower than the reference voltage Vref2, the PWM control circuit 524 sets to a high value the duty (duty cycle) of the PWM signal to be provided to the switching element so that the inductor current can be increased and the output voltage can become higher. On the other hand, when the output voltage becomes higher than the reference voltage Vref2, the PWM control circuit 524 sets to a low value the duty of the PWM signal so that the inductor current can be reduced and the output voltage can become lower. Thus, the output voltage can be can be maintained at a constant level. When the PWM control circuit 524 detects an overcurrent based on the output from the amplifier 522, it reduces the duty of the PWM signal or forcibly turns off the switching element.
The signal transmission/reception unit 530 includes a comparator, etc. for detecting a sudden decrease of an output voltage and generating an alarm signal. The signal transmission/reception unit 530 further includes the function of receiving a signal input from a high-order appliance.
Thus, the configuration for managing and controlling the operations of the power supply apparatus using a processor, etc. has been conventionally known. However, the output from the conventional charger or each DC power supply provided in a power supply apparatus has been individually adjusted under analog control.
The above described conventional power supply apparatus has the following problems.
(1) There has been remarkable progress in digital technology, and the performance of a processor has been greatly improved. As a result, a user can easily obtain a high-performance but inexpensive processor. However, in the method using the above described conventional power supply apparatus, the load of the processor (throughput) is low. Therefore, the user cannot make the most of a high-performance processor.
(2) The progress of analog technology has slowed down, and it seems to be difficult to reduce the losses or the scale of a circuit. Furthermore, using an analog circuit, parts may be replaced or the wiring pattern, etc. of the power supply apparatus may be changed if the specification of the power supply apparatus is amended.
(3) In the power supply apparatus, it is difficult to realize a small and inexpensive system because it requires a number of I/O or I/F circuits for transmitting signals between the processor and other circuits.
(4) An electric power converter and an analog circuit are normally produced independently. This is another factor for high production costs.